The present invention relates to an information recording medium used for an optical disk.
Various principles are known for recording information in a thin film (recording film) by radiating a laser beam on it. Among them, a method utilizing the change of the atomic arrangement by the radiation of the laser beam such as the phase transition (also called the phase change) of the film material or the photo darkening is not substantially accompanied by the deformation of the thin film, and therefore has the advantage that an information recording medium of a two-side disk structure can be obtained by attaching two disk members directly to each other.
Generally, these information recording media are configured of a substrate, and a protective layer, a recording film of GeSbTe group, etc., a protective layer and a reflective layer formed on the substrate, and the reflectance is higher in crystal state than in amorphous state. Therefore, the absorption of a recording film is larger for amorphus. The recording mark portion in amorphous state is liable to increase in temperature more easily than the crystal. In the case where an overwrite operation is performed in this state, therefore, a newly recorded mark is increased excessively, thereby causing the reproduction signal to be distorted.
In order to prevent this inconvenience, an effort has been made to increase the absorption coefficient of the recording film in crystal state as compared with that of the recording film in amorphous state. For example, reference 1 xe2x80x9cYamada and three others, Shingaku Giho MR92-71, CPM92-148, December 1992, p.37xe2x80x9d describes a structure formed with an Au reflective layer as thin as 10 nm to reverse the absorption coefficient.
Also, reference 2 xe2x80x9cOkada and six others, Shingaku Giho MR93-53, CPM93-105, December 1993, p. 1xe2x80x9d describes a structure in which Si of 65 nm is used for the reflective layer thereby to reverse the absorption coefficient.
In this specification, the term xe2x80x9cphase changexe2x80x9d is defined to include not only the phase change between crystal and amorphus but also between melting (change to liquid phase) and recrystallization and between crystal states.
In all the conventional information recording media used as a high-density rewritable information recording media of phase transition type using a mark edge recording, the erase characteristic is improved by reversing the absorption coefficient (the absorption coefficient of amorphus is lower than that of crystal). These media use a material with a thin reflective layer or a material of a reflective layer through which light is transmitted or has a structure allowing light to transmit therethrough. This method poses the problem that each absorption coefficient is smaller than that of the normal disk with the absorption coefficient not reversed, resulting in a small recording sensitivity. The laser used for recording having a wavelength shorter than about 680 nm is still low in output, and if the linear speed is increased for increasing the transfer rate, the recording sensitivity tends to deteriorate. Therefore a medium of high recording sensitivity is required.
Further, the use of a thin material of a low heat conductivity for the reflective layer poses the problem that heat generated at the time of recording is not easily diffused often causing an increased jitter after a multiplicity of overwrite cycles.
Accordingly, an object of the present invention is to solve these problems and to provide an information recording medium which has a superior recording/reproduction characteristic without increasing the jitter as compared with the prior art even after the overwrite cycle for high-density recording and reproduction.
Means for solving the problems will be described below.
(1) There is provided an information recording medium comprising an information recording thin film as a recording layer formed on a substrate for recording and/or reproducing information by the change in atomic arrangement caused by the radiation of light, and at least one protective layer, wherein the protective layer and the recording layer are formed in that order from the light incidence side, followed by being formed with at least one absorption control layer.
(2) There is provided an information recording medium as described in (1), characterized in that the thickness of the absorption control layer is in the range of not less than 10 nm but not more than 50 nm. The thickness of not less than 10 nm but not more than 40 nm is more preferable.
(3) There is provided an information recording medium as described in (1), wherein at least 95% of the total number of atoms of the absorption control layer is composed of a mixture or a compound of a dielectric material and a metal element.
(4) There is provided an information recording medium as described in (1), wherein the absorption control layer is made of a material having n (refractive index) of not less than 1.2 but not more than 6, and k (extinction coefficient) not less than 0.5 but not more than 3.3. If n is not less than 1.8 but not more than 5.5, and k is not less than 0.8 but not more than 3, it is more preferable.
(5) There is provided an information recording medium as described in (1), wherein the absorption control layer is made of a material having a melting point of not less than 600xc2x0 C.
(6) There is provided an information recording medium as described in (1), characterized in that in the case where information is recorded on the recording film, the reflectance in amorphous state is lower than that in crystal state, the reflectance in amorphous state is lower than the reflectance in crystal state, and the mark size with the shortest mark recorded on a material in amorphous state is equal to or smaller than the mark size with the shortest mark recorded on a material in crystal state under the same conditions.
(7) There is provided an information recording medium as described in (1), wherein at least a heat diffusion layer is formed between the substrate and the protective layer.
(8) There is provided an information recording medium comprising an information recording thin film as a recording layer formed on a substrate for recording and/or reproducing information by the change in atomic arrangement caused by the radiation of light, at least a protective layer, at least a heat diffusion layer and at least a heat diffusion layer, characterized in that the heat diffusion layer, the protective layer and the recording layer are formed in that order from the light incidence side, followed by being formed with at least one reflective layer.
(9) There is provided an information recording medium as described in any one of (7) and (8), characterized in that at least 90% of the total number of atoms of the heat diffusion layer is composed of Alxe2x80x94O.
(10) There is provided an information recording medium as described in any one of (7) and (8), characterized in that the heat diffusion layer has a layer in which at least 90% of the total number of atoms has a composition similar to any one of (SiO2), (Al2O3), (Ta2O5), (Al2O3)xe2x80x94(SiO2), (Ta2O5)xe2x80x94(SiO2), (Al2O3)xe2x80x94(Ta2O5) and (Al2O3)xe2x80x94(SiO2)xe2x80x94(Ta2O5) or a mixture composition thereof.
(11) There is provided an information recording medium as described in any one of (7) to (8), wherein the heat diffusion layer has a layer in which at least 90% of the total number of atoms has a composition similar to any one of Bexe2x80x94O, Bxe2x80x94N, Sixe2x80x94C and Mgxe2x80x94O or a mixture composition thereof.
(12) There is provided an information recording medium as described in (1), characterized by having a structure wherein a reflection layer composed of at least one layer of a Cu alloy, an Al alloy and an Au alloy is formed on the absorption control layer.
(13) There is provided an information recording medium as described in (1) or (8), characterized in that at least one surface protect layer is formed in the boundary of the recording film.
(14) There is provided an information recording medium as described in (1) or (8), characterized in that the recording film satisfies the relation
Gex-wSbyTezMw 
where 0.10xe2x89xa6xxe2x89xa60.26, 0.18xe2x89xa6yxe2x89xa60.33, 0.52xe2x89xa6zxe2x89xa60.60, wxe2x89xa60.06 and x+y+z=1, and M is any one of Na, Mg, Al, P, S, Cl, L, Ca, Sc, Zn, Ga, As, Se, Br, Rb, Sr, Y, Zr, Nb, Ru, Rh, Cd, In, Sn, I, Cs, Ba, La, Hf, Ta, Re, Os, Ir, Hg, Tl, Pb, Th, U, Ag, Cr, W, Mo, Pt, Co, Ni, Pd, Si, Au, Cu, V, Mn, Fe, Ti and Bi.
(15) There is provided an information recording medium as described in (1) or (8), characterized in that the protective layer is made of a layer containing at least 80 mol % of ZnS.
(16) In the case where the absorption control layer is made of Moxe2x80x94(SiO2), the MO amount represents preferably not less than 42 mol % of all the components. The figure of not less than 61 mol % but not more than 90 mol % is more desirable.
The use of Cr, W, Fe, Sb, C, Zn, Mn, Ti, Co, Ge, Pt, Ni, Nb, Pd, Be or Ta as a material replacing Mo in the Moxe2x80x94(SiO2) film of the absorption control layer has produced a similar result. Among these elements, Mo, Cr and W are more preferable as they have a high melting point. Also, Pd and Pt are not very reactive with other layers and the resulting increased possible number of overwrite cycles makes these elements more preferable. When Ni, Co or Ti is used, on the other hand, an inexpensive target can be used as compared with other materials and the total production cost can be reduced.
Materials which may be used in place of SiO2 in the Moxe2x80x94(SiO2) film used for the absorption control layer include oxides including SiO, Al2O3, BeO, Bi2O3, CoO, CaO, Cr2O3, CeO2, Cu2xc2x0, CuO, CdO, Dy2O3, FeO, Fe2O3, Fe3O4, GeO, GeO2, HfO2, In2O3, La2O3, MgO, MnO, MoC2, MoO3, NbO, NbO2, NiO, PbO, PdO, SnO, SnO2, Sc2O3, SrO, ThO2, TiO2, Ti2O3F TiO, Ta2O5, TeO2, VO, V2O3, VO2, WO2, WO3, Y2O3 and ZrO2, nitrides including AlN, BN, CrN, Cr2N, GeN, HfN, Si3N4, Alxe2x80x94Sixe2x80x94N group material (such as AlSiN2), Sixe2x80x94N group material, Sixe2x80x94Oxe2x80x94N group material, TaN, TiN and ZrN, sulfides including ZnS, Sb2S3, CdS, In2S3, Ga2S3, GeS, SnS2, PbS, Bi2S3, SrS, MgS, CrS, CeS and TaS4, selenides including SnSe2, Sb2Se3, CdSe, ZnSe, Tn2Se3, Ga2Se3, GeSe, GeSe2, SnSe, PbSe and Bi2Se3, fluorides including CeF3, MgF2, CaF2, TiF3, NiF3, FeF2 and FeF3, Si, Ge, borides including TiB2, B4C, B, CrB, HfB2, TiB2 and WB, carbides including C, Cr3C2, Cr23C6, Cr7C3, Fe3C, MO2C, WC, W2C, HfC, TaC and CaC2, or a material having a composition similar to any of the materials described above or a mixture thereof.
Among these materials, the use of SiO2, Ta2O5 or Y2O3xe2x80x94ZrO2 makes it possible to use a target less expensive than when using other materials, and therefore can reduce the whole cost of production.
Al2O3 is high in heat conductivity. Therefore, a disk having a structure lacking the first reflective layer and/or the second reflective layer deteriorates the rewrite characteristic to lesser degree than when using other materials.
Also, in the case where the absorption control layer contains impurities elements not more than 5 atomic % of the components thereof, it can desirably reduce the deterioration of the rewrite characteristic. The content of not more than 2 atomic % is more preferable.
(17) A preferable material of the upper surface protect layer and the lower surface protect layer is SiO2, Al2O3 or a mixture of Al2O3 and SiO2. In the case where 70 mol % or more of SiO2 or Al2O3 is contained, the crystallization rate is increased and at 18 m/s that is the rate about twice as high as in the absence of the surface protect layer, the erasure ratio reaches 25 dB or more.
The next preferable choice is Ta2O5 or a mixture between Ta2O5 and SiO2 or Al2O3. The second next preferable choice is ZrO2xe2x80x94Y2O3, SiO2 or a mixture of ZrO2xe2x80x94Y2O3 or SiO2 with Al2O3 or Ta2O5. Among these materials, Al2O3 is more preferable as it can suppress the variations of the reflectance level to 5% or less and can reduce the jitter after a multiplicity of overwrite cycles. The materials CoO, Cr2O3 and NiO are also more preferable as a uniform crystal grain size is obtained at the time of initial crystallization and the jitter is increased to a lesser degree in the initial stage of overwrite cycle.
Also, nitrides such as AlN, BN, CrN, Cr2N, GeN, HfN, Si3N4, Alxe2x80x94Snxe2x80x94N group material (such as AlSiN2), Sixe2x80x94N group material, Sixe2x80x94Oxe2x80x94N group material, TaN, TiN and ZrN are more preferable as they increase the adhesion and deteriorate the information recording medium to a lesser degree under external shocks. A material of the recording film containing nitrogen or a material having a similar composition can also improve the adhesion.
In addition, oxides such as BeO, Bi2O3, CeO2, Cu2O, CuO, CdO, Dy2O3, FeO, Fe2O3, Fe3O4, GeO, GeO2, HfO2, In2O3, La2O3, MgO, MnO, MoO2, MoO3, NbO, NbO2, PbO, PdO, SnO, SnO2, Sc2O3, SrO, ThO2, TiO2, Ti2O3, TiO, TeO2, VO, V2O3, VO2, WO2 and WO3 or carbides such as C, Cr3C2, Cr23C6, Cr7C3. Fe3C, Mo2C, WC, W2C, HfC, TaC and CaC2 or materials having a similar composition can also be used.
As another alternative, any mixture of these materials is usable.
The upper surface protect layer, the lower surface protect layer, and the replacement materials of the upper surface protect layer and the lower surface protect layer preferably represent 90% or more of the total number of atoms of the respective surface protect layer. In the case where impurities other than the materials described above reach ten atomic % or more, the possible number of overwrite cycles is reduced by 50% or more, or otherwise the rewrite characteristic is deteriorated.
In the absence of the upper surface protect layer, the reflective layer material diffuses into the recording film and the remanence increases, the reduction in the reflectance level after 100 thousand overwrite cycles can be suppressed to as small as 5% or less. A change in reflectance level causes the offset of the reproduction signal level, and adds the offset jitter for an increased jitter. Thus, the variation of the reflectance level is preferably as small as possible.
Further, for the modulation degree to be maintained at 43% or more, the figure of not more than 12 nm is preferable. For the figure of 5 nm or less, the modulation degree of 47% or more can be secured. A film of uniform thickness can be formed when the thickness is not less than about 2 nm. In the case where the thickness of the upper surface protect layer is 2 to 12 nm, therefore, the recording/reproduction characteristic is desirably improved.
In the absence of the lower surface protect layer, the protective layer material diffuses into the recording film for an increased remanence, so that the jitter increases beyond 6% after 100 thousand overwrite cycles. Further, for maintaining the modulation degree at 43% or more, the thickness is desirably maintained at 25 nm or less. The thickness of not less than 5 nm but not more than to 10 nm can secure the modulation degree of 47% or more. In view of the fact that a uniform film is formed for the thickness of about 2 nm or more, the recording/reproduction characteristic is desirably improved when the thickness of the lower surface protect layer is 2 to 25 nm. (18) Materials of the protective layer include any one of ZnS, Sixe2x80x94N group material, Sixe2x80x94Oxe2x80x94N group material, oxides such as SiO2, SiO, TiO2, Al2O3, Y2O3, CeO2, La2O3, In2O3, GeO, GeO2, PbO, SnO, SnO2, BeO, Bi2O3, TeO2, WO2, WO3, Sc2O3, Ta2O5, ZrO2, Cu2O and MgO, nitrides such as TaN, AlN, BN, Si3N4, GeN, Alxe2x80x94Snxe2x80x94N group material (such as AlSiN2), sulfides such as ZnS, Sb2S3, CdS, In2S3, Ga2S3, GeS, SnS2, PbS and Bi2S3, selenides such as SnSe2, Sb2Se3, CdSe, ZnSe, In2Se3, Ga2Se3, GeSe, GeSe2, SnSe, PbSe and Bi2Se3, fluorides such as CeF3, MgF2 and CaF2, or Si, Ge, TiB2, B4C, B, C or materials having a similar composition to the materials described above. Also, a layer of a mixtures a multi-layer of these materials including ZnSxe2x80x94SiO2 and ZnSxe2x80x94Al2O3 may be used. Among these materials, ZnS has a large n and can maintain a large modulation degree. In the case of a mixture containing 60 mol % or more of this material, the large n of ZnS and the superior chemical stability of the oxide have a combined effect. Further, ZnS has a large sputter rate, so that when ZnS represents 80 mol % or more, the film-producing time can be shortened. Other sulfides and selenides can also produce similar characteristics.
The element ratio in these compounds, i.e. the ratio between a metal element and oxygen element for oxides and the ratio between a metal element and a sulfide element for sulfides, for example, is preferably 2 to 3 or thereabouts for Al2O3, Y2O3 and La2O3, 1 to 2 or thereabouts for SiO2, ZrO2 and GeO2, 2 to 5 or thereabouts for Ta2O5 and 1 to 1 or thereabouts for ZnS. Even a ratio departing from the ratios specified above can product a similar effect. In the case where the ratio is not an integral one described above, for example, the deviation of the ratio between Al and 0 in Alxe2x80x94O is preferably not more than xc2x110 atomic % in terms of Al amount from Al2O3, the deviation of the ratio between Si and I in Sixe2x80x94O is preferably not more than xc2x110 atomic % in terms of Si amount from SiO2. In this way, the deviation of not more than 10 atomic % is desirable. A deviation of not less than 10 atomic % would change the optical characteristic and the modulation degree is reduced by 10% or more.
The protective layer and the replacement material of the protective material preferably represents at least 90% of the total number of atoms of the respective protective layer. In the case where impurities other than these materials increase to 10 atomic % or more, the possible number of overwrite cycles is reduced to one half or less or otherwise the rewrite characteristic is deteriorated.
The thickness of the protective layer is desirably 20 to 70 nm, which can increase the modulation degree for recording to as high as 43% or more, and more preferably, the thickness of the protective layer is 35 to 60 nm.
(19) The preferable materials of the heat diffusion layer are Al2O3, MgO, BeO, SiC, BN, B4C large in heat conductivity. Also, Ta2O3, SiO2, Al2O3 and mixtures thereof have an inexpensive target and the production cost thereof is desirably low. On the other hand, ThO2, TiO2, AlN and TiN are desirable for their ease to form into a film.
Other preferable materials than those described above have a heat conductivity larger than the substrate material and an absorption coefficient k smaller than 0.5.
A large heat conductivity can suppress the damage to the substrate surface by heat at the time of recording, and therefore the jitter can be suppressed to a low level after 100 thousand overwrite cycles. Also, a small k can suppress the reduction of modulation degree to a small level.
The heat diffusion layer and the replacement materials of the heat diffusion layer are desirably not less than 90% of the total number of atoms of each protective layer. In the case where the impurities other than the materials described above reaches 10 atomic % or more, the possible number of overwrite cycles is reduced to one half or less or otherwise the rewrite characteristic is deteriorated.
The thickness of the heat diffusion layer is preferably 10 to 50 nm or more preferably 20 to 40 nm.
(20) The preferable material of the first reflective layer is Alxe2x80x94Cr, Alxe2x80x94Ti, Alxe2x80x94Ag or the like containing an Al alloy which can reduce the jitter to a low level at the time of overwrite operation.
The characteristic for a multiplicity of overwrite cycles has been found to be improved when the contents of the element other than Al in the Al alloy reaches the range of not less than 5 atomic % but not more than 30 atomic %. A similar characteristic is obtained also from the Al alloy other than those described above.
A layer may be used which is composed of any one of the element unit Au, Ag, Cu, Ni, Fe, Co, Cr, Ti, Pd, Pt, W, Ta, Mo, Sb, Bi, Dy, Cd, Mn, Mg or V or an alloy containing any one of these materials as a main component such as an Au alloy, Ag alloy, Cu alloy, Pd alloy, Pt alloy, Sbxe2x80x94Bi, SUS, Nixe2x80x94Cr or alloys between these alloys. In this way, the first reflective layer is composed of a metal element, a metalloid element, an alloy or a mixture thereof.
Among these materials, such materials as Cu alloy, Al alloy or Au alloy having a large reflectance increases the modulation degree leading to a superior reproduction characteristic. A similar characteristic is exhibited by the Ag alloy. In this case, if the content of elements other than the main components is in the range of not less than 5 atomic % but not more than 30 atomic % like the Al alloy, the rewrite characteristic is improved further.
The preferable material of the second reflective layer is Alxe2x80x94Ti, Alxe2x80x94Ag, Alxe2x80x94Cu, Alxe2x80x94Cr or the like material containing an Al alloy as a main component. Al can also be used.
From this, it has been found that when the content of elements other than Al in the Al alloy is in the range of not less than 0.5 atomic % but not more than to 4 atomic %, the characteristic of a multiplicity of overwrite cycles and the bit error rate are improved, and the improvement is further enhanced in the case where the content is in the range of not less than one atomic % but not more than two atomic %. A similar characteristic is obtained for other Al alloys than described above.
Also, a layer may be used which is composed of the element unit such as Au, Ag, Cu, Ni, Fe, Co, Cr, Ti, Pd, Pt, W, Ta, Mo, Sb, Bi, Dy, Cd, Mn, Mg or V or an alloy containing any one of these elements as a main component such as an Au alloy, Ag alloy, Cu alloy, Pd alloy or Pt alloy or an alloy between these alloys. In this way, the second reflective layer is composed of a metal element, a metalloid element, an alloy or a mixture thereof.
Among these materials, those having a large heat conductivity such as Cu, Al, Au, Cu alloy, Al alloy and Au alloy have a superior rewrite characteristic as the disk can be cooled rapidly with ease. A similar characteristic is observed also for Ag and Ag alloy. In the case where the content of the elements other than Cu, Au and Ag making up the main components, like the Al alloy, is in the range of not less than 0.5 atomic % but not more than 4 atomic %, the characteristic of a multiplicity of overwrite cycles and the bit error rate are improved. This trend is further enhanced when the content is in the range of not less than one atomic % but not more than 2 atomic %.
Also, a study of the refractive index (n) and the extinction coefficient (k) of the materials of the first reflective layer and the second reflective layer described above shows that the jitter increase after 100 thousand overwrite cycles can be suppressed within 3% in the case where n of the first reflective layer is larger than n of the second reflective layer and k of the first reflective layer is smaller than k of the second reflective layer.
The materials of the first reflective layer and the second reflective layer desirably represent at least 95% of the total number of atoms of the respective reflective layer. In the case where impurities other than the materials described above reach 5 atomic % or more, the possible number of overwrite cycles is reduced to one half or otherwise the rewrite characteristic is deteriorated.
The thickness of the first reflective layer is desirably not less than 5 nm but not more than 100 nm. The thickness of the second reflective layer, on the other hand, is desirably not less than 30 nm but not more than 200 nm.
Examples of desirable combinations of the materials of the first reflective layer and the second reflective layer are an Al94Cr6 for the first reflective layer with Al99Ti1 for the second reflective layer, Al90Ti10 for the first reflective layer with Al98Ti2 for the second reflective layer, Al75Ti25 for the first reflective layer with Al99Ti1 for the second reflective layer, etc. in which case the first reflective layer and the second reflective layer contain the same main component element, and elements other than the main component element of Al are contained more in the second reflective layer than in the first reflective layer. A similar characteristic is obtained from the combinations of Alxe2x80x94Ti with Alxe2x80x94Ti, Alxe2x80x94Cr with Alxe2x80x94Cr or other combinations such as Alxe2x80x94Ag with Alxe2x80x94Cu in which the Al alloy is a main component. The Au alloy, Ag alloy, Cu alloy or a similar composition can improve the rewrite characteristic of a multiplicity of overwrite cycles.
(21) The substrate material may be a polycarbonate substrate with a tracking groove formed directly in the surface thereof, polyolefin, epoxy, acrylic resin, or a chemically reinforced glass having the surface thereof formed with an ultraviolet setting resin layer.
The substrate having a tracking groove is the one with the whole or part of the substrate surface having a groove at least xcex/10nxe2x80x2 (nxe2x80x2: refractive index of the substrate material) deep where xcex is the recording/reproduction wavelength. The groove may be formed either continuously over the whole periphery or segmented midway. It has been found that crosstalks are desirably reduced when the groove depth is about xcex/6nxe2x80x2. Further, it has been found that although the yield for substrate production is deteriorated but the cross erase is reduced desirably when the groove is deeper than about xcex/3nxe2x80x2.
Also, the groove may have different widths at different places. A substrate of sample servo format lacking a groove or of other tracking types or formats will do. A substrate having a format capable or recording and reproduction in both grooves and lands or a substrate having a format capable of recording and reproduction only in grooves or lands can also be used. The disk size is not limited to 12 cm, but other sizes including 13 cm, 3.5xe2x80x2, 2.5xe2x80x2, etc. are applicable with equal effect. The disk thickness is neither limited to 0.6 mm but other thickness such as 1.2 mm or 0.8 mm can be employed.
Two disk members including a first disk member and a second disk member are fabricated by exactly the same method, and are attached to each other by an adhesive with the second reflective layers thereof face to face. As an alternative, the second disk member may be replaced by a disk member of another configuration or a protective substrate. In the case where the disk member used for attachment or the protective substrate has a large transmittance in the ultraviolet wavelength area, the ultraviolet setting resin may be used for attaching the disk members. Other methods of attaching may also be used. A disk member of a structure having no second reflective layer may be attached with an adhesive layer formed on the topmost layer.
The first and second disk members described above are attached to each other with the second reflective layers thereof face to face through the adhesive layer. The error rate is reduced further by coating the ultraviolet setting resin about 10 xcexcm thick on the second reflective layers of the first and second disk members beforehand and attaching the disk members to each other after the resin is set.
Instead of attaching the first and second disk members to each other, the ultraviolet setting resin may be coated to the thickness of about 10 xcexcm on the second reflective layer of the first disk member. In the case of a disk member of a structure lacking the second reflective layer, the ultraviolet setting resin may be applied on the topmost layer.
(22) In addition to the structures described above, the structures of the disks 1 to 39 described below have a smaller remanence due to the absorption control layer and have the effect of reducing the jitter.
Disk 1: Substrate 1, heat diffusion layer 2, protective layer 3, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, adhesive layer 10
Disk 2: Substrate 1, heat diffusion layer 2, protective layer 3, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, second reflective layer 9, adhesive layer 10
Disk 3: Substrate 1, heat diffusion layer 2, protective layer 3, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, adhesive layer 10
Disk 4: Substrate 1, heat diffusion layer 2, protective layer 3, lower surface protect layer 4, recording film 5, absorption control layer 7, first reflective layer 8, second reflective layer 9, adhesive layer 10
Disk 5: Substrate 1, heat diffusion layer 2, protective layer 3, lower surface protect layer 4, recording film 5, absorption control layer 7, first reflective layer s, adhesive layer 10
Disk 6: Substrate 1, heat diffusion layer 2, protective layer 3, lower surface protect layer 4, recording film 5, absorption control layer 7, second reflective layer 9, adhesive layer 10
Disk 7: Substrate 1, heat diffusion layer 2, protective layer 3, lower surface protect layer 4, recording film 5, absorption control layer 7, adhesive layer 10
Disk 8: Substrate 1, heat diffusion layer 2, protective layer 3, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, second reflective layer 9, adhesive layer 10
Disk 9: Substrate 1, heat diffusion layer 2, protective layer 3, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, adhesive layer 10
Disk 10: Substrate 1, heat diffusion layer 2, protective layer 3, recording film 5, upper surface protect layer 6, absorption control layer 7, second reflective layer 9, adhesive layer 10
Disk 11: Substrate 1, heat diffusion layer 2, protective layer 3, recording film 5, upper surface protect layer 6, absorption control layer 7, adhesive layer 10
Disk 12: Substrate 1, heat diffusion layer 2, protective layer 3, recording film 5, absorption control layer 7, first reflective layer 8, second reflective layer 9, adhesive layer 10
Disk 13: Substrate 1, heat diffusion layer 2, protective layer 3, recording film 5, absorption control layer 7, first reflective layer 8, adhesive layer 10
Disk 14: Substrate 1, heat diffusion layer 2, protective layer 3, recording film 5, absorption control layer 7, first reflective layer 8, second reflective layer 9, adhesive layer 10
Disk 15: Substrate 1, heat diffusion layer 2, protective layer 3, recording film 5, absorption control layer 7, adhesive layer 10
Disk 16: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, second reflective layer 9, adhesive layer 10
Disk 17: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, adhesive layer 10
Disk 18: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, second reflective layer 9, adhesive layer 10
Disk 19: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, adhesive layer 10
Disk 20: Substrate 1, heat diffusion layer 2, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, second reflective layer 9, adhesive layer 10
Disk 21: Substrate 1, heat diffusion layer 2, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, adhesive layer 10
Disk 22: Substrate 1, heat diffusion layer 2, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, second reflective layer 9, adhesive layer 10
Disk 23: Substrate 1, heat diffusion layer 2, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, adhesive layer 10
Disk 24: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, second reflective layer 9, adhesive layer 10
Disk 25: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, adhesive layer 10
Disk 26: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, second reflective layer 9, adhesive layer 10
Disk 27: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, upper surface protect layer 6, absorption control layer 7, adhesive layer 10
Disk 28: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, absorption control layer 7, first reflective layer 8, second reflective layer 9, adhesive layer 10
Disk 29: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, absorption control layer 7, first reflective layer 8, second reflective layer 9, adhesive layer 10
Disk 30: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, absorption control layer 7, first reflective layer 8, adhesive layer 10
Disk 31: Substrate 1, protective layer 3, lower surface protect layer 4, recording film 5, absorption control layer 7, adhesive layer 10
Disk 32: Substrate 1, protective layer 3, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, second reflective layer 9, adhesive layer 10
Disk 33: Substrate 1, protective layer 3, recording film 5, upper surface protect layer 6, absorption control layer 7, second reflective layer 9, adhesive layer 10
Disk 34: Substrate 1, protective layer 3, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, adhesive layer 10
Disk 35: Substrate 1, protective layer 3, recording film 5, upper surface protect layer 6, absorption control layer 7, adhesive layer 10
Disk 36: Substrate 1, protective layer 3, recording film 5, upper surface protect layer 6, absorption control layer 7, first reflective layer 8, second reflective layer 9, adhesive layer 10
Disk 37: Substrate 1, protective layer 3, recording film 5, absorption control layer 7, second reflective layer 9, adhesive layer 10
Disk 38: Substrate 1, protective layer 3, recording film 5, absorption control layer 7, first reflective layer 8, adhesive layer 10
Disk 39: Substrate 1, protective layer 3, recording film 5, absorption control layer 7, adhesive layer 10
(23) The recording/reproduction characteristic is improved simply by securing a desired range of thickness or material of each layer independently. A higher effect can be achieved, however, by combining the desired ranges of the respective factors.
(24) A better characteristic is obtained in the case where the recording film has a composition defined as 0.12xe2x89xa6xxe2x89xa60.24, 0.20xe2x89xa6yxe2x89xa60.31, 0.54xe2x89xa6zxe2x89xa658, 0xe2x89xa6wxe2x89xa60.04.
Further, in the case where the Ge amount reaches not less than 20 atomic % in this range, the read light endurance is improved by 1.5 times. The read light endurance is obtained by determining, and by comparison with, the power of the read light for reducing the recording signal by 2 dB or more during a five-minute reproduction. For the Ge amount of not more than 17 atomic %, on the other hand, the extinction ratio is large also in the case where the linear speed is high, thus producing a superior figure of not less than 30 dB for 12 m/s.
In the case where M is Ag, the recording sensitivity is improved by 10% as compared with Gexe2x80x94Sbxe2x80x94Te. In the case where M is at least one of Cr, W and Mo, on the other hand, the possible number of overwrite cycles at which the jitter increases at least 5% is improved three times or more in a multiplicity of overwrite cycles, as compared with Gexe2x80x94Sbxe2x80x94Te. In the case where M is at least one of Pt, Co and Pd, the crystallization temperature is increased by at least 50xc2x0 C. as compared with Gexe2x80x94Sbxe2x80x94Te.
Also, in the case where the impurities elements in the recording film are not more than 5 atomic %, the deterioration of the rewrite characteristic can be reduced desirably. The figure of not more than 2 atomic % produces a more desirable result.
The thickness of the recording film is desirably not less than 10 nm but not more than 30 nm, and the figure of not less than 13 nm but not more than 20 nm is more desirable.
Though somewhat time-consuming, mixing nitrogen with the sputtering gas at the start or end of the fabrication process of the recording film or using a target mixed with a small amount of nitrogen in the composition of the recording film or otherwise containing nitrogen in the neighborhood of the boundary between the recording film and other layers improves the adhesion for an improved characteristic.